Published Examined Japanese Utility Model Application SHO 41-1925 discloses a reversible rotary cultivating apparatus wherein tines adapted for cultivation by reversible rotation and each including a forward edge portion and a reverse edge portion at opposite sides of the blade portion thereof are attached to a reversibly rotatable tine shaft. In accordance with the kind of crop to be grown or field condition, the tine shaft is rotated about a lateral axis forward or reversely to selectively perform forward-rotation cultivation (downcutting) or reverse-rotation cultivation (upcutting).
With this conventional apparatus, the forward and reverse edge portions of each tine have curved edge lines which are identically shaped symmetrically for forward rotation and reverse rotation and are identical in cutting angle at any optional point along the edge line, so that reverse-rotation cultivation requires much greater power consumption than forward-rotation cultivation.
When the apparatus cultivates by forward rotation, the tines break up lumps of soil and throw the soil rearward opposite to the direction of advance of the apparatus without carrying the soil forward toward the advancing direction, whereas during reverse-rotation cultivation, the broken soil is raised at the front side of the tine shaft and thereafter thrown rearward with the revolution of the tines. Thus, the tines interfere with the soil for a longer period of time in the latter case. Since the forward and reverse edge portions of the convention tine are curved identically, the power consumption is greater in the latter case than in the former case by an amount corresponding to the increase in the period of interference.
For example, when an apparatus of the type described was operated with the tine shaft driven at about 169 to 171 r.p.m. for reverse rotation or at about 179 r.p.m. for forward rotation to measure the average power PS required of the PTO shaft of the tractor relative to the pitch of cultivation, P, the power consumption was much greater for reverse-rotation cultivation C than for forward-rotation cultivation B as shown in FIG. 1.